Having solved the phase problem at 3.3A resolution for the octameric histone core of the nucleosome by iterated single isomorphous replacement with solvent flattening and anomolous dispersion, it is proposed to fit the amino acid sequences to the electron density map and extend the resolution of 2.8A. Having solved the phase problem for the carbon omonoxide complex of both the dimeric and tetrameric hemoglobins of the blood claim Scafarca inaequivalvis by a combination of multiple heavy atom isomorphous replacement, symmetry averaging and molecular replacement, it is proposed to fit the amino acid sequences to the electron density maps and extend the resolution to at least 2.0A. It is also proposed to prepare crystals of the dimeric and tetrameric deoxy clam hemoglobins and to determine their structures so that the structural alterations accompanying cooperative ligand binding can be seen. It is proposed to refine the structures of deoxy and carbon monoxide Glycera hemoglobin at 1.5A resolution in order to define the structural alterations that accompany ligand binding in a monomeric hemoglobin lacking a distal histidine.